Pakistan's Prime Minister, Nawaz Sharif, has led condemnation of the killing of leading human rights activist Sabeen Mehmud.
Sabeen Mehmud was shot dead in Karachi as she drove home with her mother, who was injured in the attack.A statement from Mr Sharif's office expressed condolences and ordered an immediate investigation.
No group has yet said it carried out the killing; the campaigner been subject to death threats before.
"It's an incident of targeted killing," said Dr Jamil Ahmed, the Karachi-South Deputy Inspector General of Police, who said it was too early to establish a motive, Dawn newspaper reported.
Her killing came hours after she hosted a talk on the Pakistani army's alleged involvement in the torture and killing of political activists in restive Balochistan province.
The talk was originally due to be held earlier this month at a university in Lahore but authorities cancelled it.
Ms Mehmud, 38, was a director of the charity The Second Floor, also known as T2F.
T2F regularly holds seminars on human rights issues. It houses a cafe and book shop where Karachi's liberal activists and students can meet.